Clear terpolymers



Sept. 30, 1958 R. J. sLocoMBE ET AL 2,854,439 v CLEAR TERPOLYMERS Filed Dec. '7, 1953 2 Sheets-sheet 1 foam# J. Loco/s @zopas L. awp

INVENToRs.

y Filed Dec. 7, 1953 Sept. 30, 1958 RL J. sLocoMBE ET AL 2,854,439

CLEAR TERPOLYMERS 2 Sheets-Sheet 2 AVA A AVAVAVAYA VV V V WMM NVM-ANW /VWWMW /VVQ/A/f-f AAAAAA am isf M VAYA VVV United States Patent() CLEAR TERPOLYMERS Robert J. Slocombe, Dayton, and George L. Wesp, Engle- Application December 7, 1953, Serial No. 396,484 23 Claims. (Cl. 260-80.7)

This invention relates to three-component inter polymers, commonly called terpolymers, i. e., interpolymers prepared by polymerizing 1a monomeric mixture consisting of three different monomers. In specific aspects the invention pertains to terpolymers of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene, amethylstyrene, isoprene, butadiene, and (c) a diierent monomer selected from said group. Other aspects of the invention relate to improved methods of preparing clear terpolymers.

It is by now well known that ethylenically unsaturated monomers differ greatly in their polymerization reactivity toward each other. There are in fact some monomers that will not undergo homopolymerization at all, i. e., polymerization of two or more molecules of the same monomer to form a polymer of that monomer, yet will .readily undergo interpolymerization with certain other monomers. interpolymerization affords a method of imparting varying characteristics to a polymer, and in many instances such characteristics cannot be obtained by mere physical admixture of two or more homopolymers. However, because of the above-mentioned dierences in reactivity among monomers toward each other, marked heterogeneity is the rule in interpolymers and only under special circumstances can 'an interpolymer be obtained 'that is of suicient homogeneity to give a transparent or clear interpolymer. While some objectionable properties such as color, encountered in interpolymers, can 4often be avoided by means such as the use of stabilizers` or lower polymerization temperatures, incompatibilitymanifested by haze, turbidity, or opacity in plastics is not overcome by such treatment.

If a monomeric mixture is subjected to polymerization and the initial increment of polymer is segregated before the polymerization is preciable extent, it is frequently possible to obtain a clear' interpolymer, but the commercial impracticability of such a procedure is apparent. On the other hand, if polymeri zation is permitted to proceed to 'a considerable andv especially to a high degree of conversion, Vactive monomer enters into the polymer to a greater extent than a less reactive monomer or monomers with the consequence that residual unreacted monomer be comes more and more depleted in the more reactive monomer, while the polymer being formed in the latterA stages of polymerization is deficient in the more reactive monomer. There results a polymeric material which isl made up of a variety of polymer molecules running a gamut of compositions such that the total polymer isr heterogeneous with resultant opacity and often greatly' impaired physical properties. This phenomenon, result-- ing in an undesirable product, can be overcome to an, appreciable but limited extent by gradually adding dur-4 ing the course of the polymerization the more reactivemonomer at a rate aimed at keeping the composition of unreacted monomeric mixture essentially constant. Asr

a practical matter it is extremely diflicult to approach.

allowed to go forward to an apthe more re- 2,854,439 Patented Sept. 30, 1958 ice uniformity in such an operation, and it is impossible to use this technique -at all in the case of mass (bulk) polymerization in which the polymerization reaction mix'- ture sets up into semi-solid or solid polymer after the reaction is only partly completed so that further access of added monomer to the total mixture cannot be obtained.

It is only in recent years that systematic laboratory and theoretical studies of interpolymerization have gone forward sufficiently to permit acertain amount of predictability in this eld. It has been theorized that in a simple binary system involving the free-radical-initiated polymerization of only two monomers, the composition of polymer will be dependent only upon the rate of four propagation steps, i. e., steps in the propagation of polymer molecules. Thus, taking a system involving two monomers, M1 and M2, a growing polymer chain can have only two kinds of active terminal groups, i. e., a group derived from M1 or a group derived from M2. Either of these groups has the possibility of reacting with either M1 or with M2. Using mland m2 to indicate these active terminal groups, the four possible reactions are as follows:

Theoretical considerations lead to the now generally accepted copolymer composition equation which describes the ratio incapable, because of their respective reactivity ratios,`

of forming under any conditions an instantaneous polymer having the same composition as the monomeric mixture fromrwhich it is formed. However there are certain monomer pairs which, in a proportion characteristic of that pair, give a copolymer having the same composition as the particular monomeric mixture. In such instances, a batch polymerization can be carried out with a monomeric mixture of the particular composition with a resultant homogeneous copolymer containing the same relative proportions of the monomers as in the initial monomeric reaction mixture. This composition is known as the polymerization azeotrope composition, and is represented by the equation:

Such an azeotrope composition can exist only for those r2 are less than one,v

possible, and for each of these 160,000 combinations the variations in relative proportions of three monomers arel infinite. If the assumptions made in the development off the copolymer composition equation still hold true where three monomers are to be interpolymerized, it is apparent that the composition of the terpolymers formed at any given instance will now be dependent upon the rate of nine propogation steps which are dependent upon` thev relative concentrations of the monomers in the monomeric mixture and the reactivity ratio between each of the pairs of the monomers in the mixture. It has been pointed out that the study of terpolymers can be simplified somewhat by application of the copolymer composition equation, suitably modilied for three-component systems, so as to eliminate from consideration monomers whose ability to interpolymerize is so slight that further investigation of such combinations is obviously not warranted. However, the discovery of terpolymers having particularly desired physical properties has to the present time been limited to the needle in the haystack type of investigation. There is an obvious need for some procedure in the terpolymer field whereby terpolymers of particular properties can be made with a reasonable degree of predictability.

In accordance with the present invention, we have found a group of terpolymers that can be made by freeradical-initiated batch polymerization and that have the very desirable property of clarity. These terpolymers are made by polymerizing a monomeric mixture of certain proportions of three monomers. The proportions giving clear terpolymers will vary from one monomeric mixture to another depending upon the particular monomers present in that mixture. The invention is particularly applied to monomeric mixtures consisting essentially of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene, a-methylstyrene, isoprene, butadiene, and (c) a different monomer selected from the same group listed under (b). For example, a monomeric mixture consisting of methacrylonitrile, vinyltoluene, and isoprene will, when subjected to free-radical-initiated batch polymerization, give a clear terpolymer only if the relative proportions of methacrylonitrile, vinyltoluene, and isoprene are properly chosen in a manner to be hereinafter described. In contrast, a monomeric mixture consisting of methacrylonitrile, styrene, and a-methylstyrene will give a clear terpolymer on Ibeing subjected to free radical batch polymerization only if the relative proportions of the three mentioned monomers in the monomeric mixture are within certain limits which in general are different from those of the aforementioned mixtures of methacrylonitrile, vinyltoluene and isoprene, and yet which are chosen in accordance with the same principle now to be discussed.

We have found that clear terpolymers of the nature described are made provided the proportions of three monomers in the monomeric mixture are chosen from the area lying along the line joining the binary polymerizations azeotrope composition of methacrylonitrile and the particular (b) on the one hand and the binary polymerization azeotrope composition of methacrylonitrile and the particular (c) on the other hand, as plotted on a triangular coordinate graph. By way of example, taking the case where (b) is vinyltoluene and (c) is isoprene, the point of the lbinary azeotrope composition of methacrylonitrile and vinyltoluene is placed along one side of a triangular coordinate graph Iat the proper location between the apex designating 100 percent methacrylonitrile '4 and the apex designating 100 percent vinyltoluene. This point is 32.1 weight percent methacrylonitrile and 67.9 weight percent vinyltoluene. On the opposite side of the equilateral triangle, constituting the triangular coordinate graph, is placed the point representing the binary azeotrope composition of rnethacrylonitrile and isoprene, this, of course, being located at the proper position on the side of the triangle between the apex representing 100 percent methacrylonitrile and the apex representing percent isoprene. This point is approximately 39.6 weight percent methacrylonitrile and 60.4 weight percent isoprene. Now a straight line is drawn between these two points. This line cuts across the triangular coordinate graph, without touching the side of the triangle opposite the methacrylonitrile apex, which side represents varying proportions of vinyltoluene and isoprene in binary mixtures of same. Vinyltoluene and isoprene do not form a binary azeotrope. The said straight line joining the two points of binary azeotrope compositions describes three-component monomeric mixtures which, when subjected to free-radical-initiated batch polymerization, give clear terpolymers. Further, there is an ap- -preciable area lying on each side of said line in which the terpolymers are essentially clear. However, one cannot go too far from this line without producing terpolymers which are not clear but range from hazy to opaque materials. The invention particularly applies to the area lying within 5 percent on each side of said line; said 5 percent is measured on the graph in a direction normal to the line, and is equal to tive one-hundredths of the shortest distance between an apex and the side of the triangle opposite the apex. Another way of saying the same thing is that the invention particularly applies to the area of the graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line. Terpolymers made by polymerizing a monomeric mixture having a composition lying in the area within 5 percent on each side of the line joining the two binary polymerization azeotrope compositions, are generally clearer than polymers made from similar monomeric mixtures lying farther away from and on the same side of the line. In most systems all terpolymers made from monomeric mixtures having compositions in the area lying within 5 percent on each side of the line are clear. In some systems the area of clarity may not extend as far as 5 percent from the line. Those skilled in the art, having had the benefit of the present disclosure, can easily determine by simple tests of the nature described herein which monomeric mixtures give clear terpolymers in a given polymerization system. In all events, the compositions of monomeric mixtures giving clear terpolymers will be found to constitute an 'area lying along and encompassing the line joining the two binary polymerization azeotrope compositions.

The reasons for the clarity of terpolymers made as described are not known. The line joining the two binary azeotrope compositions does not represent what might be called a series of three-component azeotropes. From much detailed data which we have obtained, the relative proportions of the three monomers in terpolymers made from monomeric mixtures lying along said line are not identical to the monomeric mixture from which the terpolymer is being prepared. In other words, during the course of a batch polymerization of a monomeric mixture whose composition is taken from the line, the composition of residual monomeric material drifts and the terpolymers so formed are not homogeneous mixtures of polymer molecules all of which contain monomer units in the same ratio, but rather are mixtures of polymer molecules having varying proportions of the three monomer units therein. No heretofore known scientific facts or theories of interpolymerization explain our discovery. However, regardless of the various reasons for believing that terpolymers made from compositions lying along thepline as-.jaforesaid wouldA bei graphs showing compositionseof somethree-component.

monomeric mixtures that give clear terpolymers on being subjected to free-radical-initiatecl batch polymerization. Figure I represents the system `ymethacrylonitrile/vinyltoluene/isoprene.

Figure II represents the system "methacrylonitrile/ styrene/ -methylstyrene. i

By the present invention we can subject a given monomeric mixture consisting of three monomers, selected as described herein, to a batch polymerization and carry the polymerization reactionto `complete or'essentially complete, say 90 to 100 percent, conversion of all of the monomers and yet obtain a clear solid resinous terpolymer. If desired, the polymerization can be stopped at any point short of completion so long as vpolymerization conditions are such as to produce solid terpolymer, but this is not necessary in order toobtain a clear terpolymer and would seldom be advantageous; The higher the degree of conversion of monomeric mixtures, the greater the advantages of our invention. This-is because the greatest extent of heterogeneity is found with complete conversion to polymers. least 50 weight percent conversion and preferably atleast 80 weightpercent conversion, is preferred in practicing the invention. However, some of the benefits of the invention may be realized even where the percentage conversion isas low as 2O percent. 'With very-low con-A versions, the polymer formed tendsto approach the per-v fect homogeneity existing in the first infinitely -small increment of polymer formed. As pointed out above, cornrnercial practicality requires that conversionbe carried to a value more than a few percent, hence introducing the lack of homogeneity which up to now, the art has not known how to avoid other than by techniques such as gradual monomer addition. It is to be recognized that f the extent of the area of clear terpolymers, lying along the line joining the two binary polymerization azeotrope compositions, is dependent not only on the particular polymerization system but also on the percentage conversion, said area being the greater the lower the percentage conversion, and the smaller the higher the percentage conversion. It is observed that theterpolymers become clearer as the composition of the monomeric mixture approaches the line joining the two binary azeotrope compositions, the general rule being that the clearest terpolymers are those derived from monomeric cornpositions lying on the line.

It is usually desirable that the three-component monomeric mixture contain at least 2 weight percent, and preferably at least 5 weight percent, of the monomer present in the smallest amount.

The invention is broadly applicable to any free-radicalinitiated interpolymerization of three-component monomeric mixtures containing the monomer combinations and inthe proportions set forth herein, provided the polymerization is carried out by a batch procedure. By this it is meant that all of the monomeric materials -to be employed are introduced simultaneously in the desired proportions into the polymerization reaction system. Ordinarily a single charge of monomeric materials will be placed in a reaction vessel and the single charge subjected to polymerization conditions until the polymerization is substantially complete. However, it is not outside the scope of our invention to introduce continuously a monomeric'mixture containing the three monomers in fixed proportions into a flow-type polymerization system, whereby the initial polymerizable mixture passes away from its point of introduction and ultimately is re- A high conversion, i. e., at`

coveredas polymer. Thiscanbe accomplished by con-A tinuous flowing of the monomeric mixture into the lirstof a series of polymerization reaction vessels with cont1nuous ow of reaction mixture from one vessel to another along a series of two or more such vessels with ultimate recovery of polymer from the last in the series.A

- additionof a monomer or monomers having a composiprocedure the reaction mixture is free from added sol=l ,vent or other reaction medium and consists solely of tion different from the initial ymonomeric mixture.

The invention is perhaps most advantageously eiected by the mass or bulkA polymerization procedure. In such monomers, resultant polymers, and catalyst and regulator, if any.' An important advantage of the invention is` that such a mass polymerization can be effected to pro-- duce'av clear terpolymer in a situation in which it is impossible touse the gradual monomer addition technique discussed above.

If desired, the nterpolymers of the present invention can be made by the suspension or the emulsion polymerization techniques. For suspension polymerization a reaction medium such as water is used together with a small amount of suspending agent, for example' tricalcium phosphate, carboxymethylcellulose, etc., to give a suspension of particles of initial monomeric mixture,- which particles are notof -such small size as to result in v,a permanently stable-latex. Where the `particles are of 35'Y quite large size, this type of polymerization is often called pear polymerization. To effect emulsion polymerization, sufficient amount of emulsifying agent, for example a-water-soluble salt of a sulfonated long chain alkyl aromatic compound, a surface active condensationproduct ofA ethylene oxide with long chain aliphatic alcohols or mercaptans, etc., is employed along with vigorous agitation whereby an emulsion of the reactants in water is formed and the product is obtained .in the form of a latex. The latex can then be coagulated if desired by known methods and the polymer sepaarted from the water. For some applications the latex can be employe-d directly as for example for forming a film, and the resultinglilm after evaporation of the water will be clear when the polymers are made in accordance with the present invention. The emulsion technique has certain advantages particularly in that a very high degree conversion of the monomers is obtained with considerable rapidityfsince the heat of reaction is easily carried off by indirect heat exchange withv the reaction mixture which contains a considerable proportion of water. Such polymerizations are often eiected with redox-type catalyst systems at moderate temperatures` of say 60 C. on down to 0 C. and below.

The polymers of the present invention can also be made in the presence of an added organic solvent. It should be recognized however that the presence of such a solvent ordinarily results in a 'polymer of lower molecular weight than that obtained in the absence of the solvent.

Conventional recipes and procedures for effecting mass, solvent, suspension and emulsion polymerizations are so well-known to those skilled in the art, that they need not be further detailed here.

From the foregoing, it will be apparent that the term, monomeric mixture, as used in the claims refers only to the polymerizable monomeric materials used in the process, and that additionally solvents, aqueous reaction media, catalysts, etc., can be present or not in the reaction mixture as may be desired in any particular case.,

In vother words, in the claims monomeric mixture is not necessarily synonymous with reaction mixture.

Polymerization can be effected by any of the wellknown free-radical mechanisms. initiated and carried on by virtue of free radicals, which can be derived from the monomers themselves on simple heating of the monomeric mixture to a suitable temperature, or can be derived from added free-radical-supplying catalysts, especially the per compounds and the azo compounds, or can lbe derived by ultraviolet or other irradiation of the reaction mixture with or without the presence of photosensitizers, e. g., organic disulfides. Examples 1 and 2 set forth hereinafter include data on thermal polymerizations in which the polymerization reaction was initiated and maintained merely by heating the monomeric mixture in the absence of any added catalyst. Additionally, Example 1 contains data on polymerizations effected in the presence of an added polymerization catalyst or initiator. In many instances it will be desired to add a suitable polymerization catalyst, in which case sufficient catalyst is employed to give a desired reaction rate. Suitable catalysts are of the free-radicalpromoting type, principal among which are peroxidetype polymerization catalysts, and azo-type polymerization catalysts. Those skilled in the art are now fully familiar with a large number of peroxide-type polymerization catalysts and a suitable one can readily be chosen by simple trial. Such catalysts can be inorganic or organic, the latter having the general formula: ROOR", wherein R is an organic radical and R is an organic radical or hydrogen. These compounds are broadly termed peroxides, and in a more specific sense are hydroperoxides when R" is hydrogen. R and R" can be hydro-` carbon radicals or organic radicals substituted with a great variety of substituents. By way of example, suitable peroxide-type catalysts include benzoyl peroxide, ditertiary butyl peroxide, tertiary butyl hydroperoxide, diacetyl peroxide, diethyl peroxycarbonate, 2-phenyl propane-2-hydroperoxide (known also as cumene hydroperoxide) among the organic peroxides; hydrogen peroxide, potassium persulfate, perborates and other per. compounds among the inorganic peroxides. The azo-type polymerization catalysts are also well-known to those skilled in the art. These are characterized by the presence in the molecule of the group -N=N bonded to one or two organic radicals, preferably lat least one of the bonds being to a tertiary carbon atom. By way of example of suitable azo-type catalysts can be mentioned 11,11 azodiisobutyronitrile, p bromobenzenediazonium tiuoborate, N-nitroso-p-bromoacetanilide, azomethane, phenyldiazonium halides, diazoaminobenzene, p-bromobenzenediazonium hydroxide, p-tolyldiazoaminobenzene. The peroxy-type or azo-type polymerization catalyst is used in small but catalytic amounts, which are generally .not in excess of one perecnt by weight based upon the monomeric material. A suitable quantity is often in the range of 0.05 to 0.5 percent by weight.

Photopolymerization is another suitable procedure for carrying out the present invention. This is ordinarily accomplished by irradiating the reaction mixture with ultraviolet light. Any suitable source of light is employed having effective amounts of light with wave lengths of 2,000 to 4,000 Angstr-om units. The vessel in which the polymerization is conducted should be transparent to light of the desired wave length so that the light can pass through the sides of the container. Suitable glasses are available commercially and include borosilicate (Pyrex), Vycor, and soft glass. Alternatively, the

source of light can be placed directly over the surface of the monomer in a container or can be placed within the reaction mixture itself. In some instances it is helpful to add a material that can be termed a photosensitizer, i. e., a material which increases the rate of photopoly- The polymerization is merization, for example organic disultides as described in U. S. Patent No. 2,460,105.

Choice of a suitable temperature for a given polymerizationwill readily be made by those skilled in the art having been given the benefit of the present disclosure. In general, suitable temperatures will be found within the range of 0 C. to 200 C., although temperatures outside this range are not beyond the scope of the invention in its broadest aspects. The time required for complete polymerization will depend not only upon the temperature but also upon the catalyst if any is employed, the ability of the system to remove heat of polymerization, and the particular monomers employed. The examples set forth hereinafter give some illustrative information as to reaction times for particular polymerizations.

The term triangular coordinate graph as used herein is well understood. The accompanying figures are examples of such graphs and the use of same. However, for the sake of completeness the following statement can be made concerning the character of such triangular graphs. The graph is au equilateral triangle, divided off by three series of parallel lines each series being parallel to one side of the triangle. The distance between an apex of the triangle and the side opposite that apex represents variations in percentages of the component designated by that apex varying from percent to 0 percent in equal increments running from the apex to the opposite side of the triangle. For example, if the distance between the apex and the side of the triangle opposite the apex is divided into 100 equal parts by lines passing across the triangle and parallel to said side, each line represents l percent of the component for which that apex is designated. Thus, any point within the triangle represents a single three-component composition, the indicated percentages of the three components totaling 100 percent.

As an aid in the choice of suitable proportions of monomers for polymerization in accordance with the invention the following data on reactivity ratios of certain monomer pairs are presented by way of example. The values given are considered the best ones represented in the literature or otherwise known, (see Copolymers by Alfrey, Bohrer and Mark, Interscience Publishers, Inc., 1952, pp. 32-43). In many instances an attempt is made to set forth an approximate order of accuracy. These latter figures, expressed as plus or minus certain values, should not however be given too much credence since such attempts to evaluate possible errors are dependent to a considerable extent on subjective evaluation of the data. Most of the values for reactivity ratios given are for moderate temperatures, say between about room temperature (20 C.) and 100 C. Of course, the value of the reactivity ratios for a monomer pair is a function of temperature but the variation in reactivity ratios with temperature is quite small and is of little importance unless the polymerization is to be carried out at temperatures considerably removed from those mentioned. Likewise, the reactivity ratios given are for atmospheric or autogenous pressure. Only if the polymerization pressure is to be quite considerably increased will there be an important change in the value of the reactivity ratios. Those skilled in the art, having been given the benefit of the present disclosure, will be able to evaluate the effect, if any, of reaction conditions on the values given herein and determine the extent of such effect. Similarly, those skilled in the art can determine by well-known procedures the correct reactivity ratios for monomer pairs not specifically set forth in the following tabulation, which tabulation is given by way of example of some but not all of the monomers that are the subject matter of the present invention.

In the following tabulation methacrylonitrile is considered as M2 and the other monomers in each instance are considered as M1. Substitution of the values for r1 and ass-1,119.6

' r2' in the equation given above for the binary polymerizapoints is drawn the line of clear terpolymers.

TABLE Ms Mi n rz styrene o 3010.10 o iico a-Methylsty-fene-- o12io.o2 53510.02 Butadiene 3610.07 o.o4i0.o4

Where M1 is to be vinyltoluene or vinylxylene, the reactivity ratios given above for methacrylonitrile/ styrene are used, on the assumption that the reactivity ratios for the systems methacrylonitrile/vinyltoluene and methacrylonitrile/vinylxylene do not differ essentially for the purposes of this invention from the reactivity ratios of the corresponding system wherein styrene is M1. This assumes that the introduction of one or two methyl groups into the aromatic nucleus of styrene does not greatly alter the polarity and steric properties of the vinyl double bond. Likewise, when isoprene is to be used, the reactivity ratios are assumedv not to diier essentially for the purposes of this invention from the above reactivity ratios involving butadiene. thel molecule from butadiene to isoprene does not greatly alter the polarity and steric properties of the vinyl double bond. Whenever weight percent rather than mole per- This assumes the change in the methacrylonitrile/vinyltoluene binary pol'yrherizationl` azeotrope as 32.1l weight percent methacrylonitrile 67.9

weight Vpercent: vinyltoluene.

Taking methacrylonitrile as M2 and isoprene as M1,

and r1 as 0.36 and r2 as 0.04 on the assumption vthat ther reactivity ratios for this binary system do not diier essentially for the purposes of this invention from those for the corresponding system methacrylonitrile/butadiene for the reasons discussed hereinabove, by the same procedure the binary polymerization azeotrope for methacrylonitrile/isoprene was calculated to be 39.6 weight percent rnethacrylonitrile, 60.4 weight percent is isoprene.

A series of monomeric mixtures was made up, each mixture being prepared by admixture of the individual pure monomers in a Pyrex test tube 150 mm. long and having an internal diameter within the approximate range of 14 to 18 mm., usually about 16 mm. Each test tube containing the particular monomeric mixture was ushed with nitrogen in order to remove any air present in the gas space above the liquid, and the test tube was then sealed oi at the top by heating the tube under nitrogen and pulling it out in the flame to seal the tube completely. Each particular monomer mixture was prepared and polymerized in duplicate. For each particular mixture, one of the tubes contained no added catalyst, while the other duplicate tube contained 0.15 weight percent cent is desired as a matter of convenience, mole percentages of the binary azeotrope compositions are easily converted to weight percent by use of the molecular weights of the particular M1 and M2.

The following examples illustrate some methods for n practicing the present invention with respect to certain ternary mixtures of monomers. The general applicability of the invention, and advantages thereof, are shown in these examples. It will be appreciated that variations can be made in the particular choice of monomers, proportions, and methods of polymerization in accordance with the general teachings of the presentspeciication, and the examples are not to be taken as coextensive with the invention in its broadest aspects.

Example 1.-This example concerns the ternary system methacrylonitrile/vinyltoluene/isoprene. The data obtained in this example are set forth graphically in Figure I of the drawings.

The -composition of the methacrylonitrile/Vinyltoluene binary azeotrope was calculated in the following manner according to the article by Mayo and Walling, Chemical Reviews, 46, 199 (1950). The reactivity ratios for this binary system were assumed not to differ essentially for the purposes of this invention from those for the corresponding system methacrylonitrile/styrene, as discussed hereinabove.

Methacrylonitrile (M2) vinyltoluene (M1) T1:

(64.5 X 100) /95.0 67.9 Weight percentvinyltoluene (30.5 X 100 [95.0: 32.1 weight percent methacrylonitrile -The foregoing calculations give the composition of hours.

azo-'bis-isobutyronitrile as polymerization catalyst (initiator).

The rate of polymerization was quite low in this system, lso a long polymerization cycle was used. The sealed tubes were placed in a 40 C. constant temperature bath and maintained thereinfor an initial period of Thereafter the tubes were progressively placed in temperature baths of increasing temperatures, in accordance with the following schedule, wherein the sample number corresponds to the sample numbers given in lTable I. Those sample numbers having a c following the number are the tubes which contained catalyst. It will be'noted that for. some of the sample numbers only the catalyst-containing tube is listed. This is because for these particular sample numbers, the tubes that contained no catalyst were so'slow in polymerizing that they were not taken through a complete polymerization cycle and therefore no final product was obtained on which observations could be made on clarity and color.

TABLE Polymerization cycle Heating Period (hrs.) at Different Temperatures Sample No.

40C 50C. 90C. 120C.`180C.

c=tube contained catalyst.

The vinyltoluene employed in these tests was a mixture of isomeric metaandpara-methylstyrene.

The various monomeric compositions are set forth in detail in Tablel. Table I designates each different.milt-v asses-Be ture by sample number. Sample No. l is. theV binary methacrylonitrile/vinyltoluene azeotrope composition. Sample No. 6 is the binary methacrylonitrile/isoprcne azeotrope composition. Samples Nos. 2, 3, 4, and have compositions which fall on a straight line connecting the two binary compositions, designated samples Nos. land 6, when plotted on triangular coordinates. See Figure I.

tween the amount oi isoprene and the softness and rub beriness of the sample, the more isoprene the more rubbery and. the less isoprene the harder the sample. It will be observed that by virtue of the present invention it is possible to prepare a terpolymer of methacrylonitrile/vinyltoluene/isoprene having a hardness or softness or rubberness chosen from a wide range of values, yet still having the desirable property of clarity.

TABLE I M ethacrylonitrile/ vinyltaluene/ soprene terpolymers Composition, Appearance Samplel No. Wt. Percent MN /V T/Ip Clarity Color Hardness 32/68/0 Hard. 32/68/0 Do. 33/60/7 Do. 35/42/23 Sott and rubbery v (not sticky). 36/32/32 C-Clear Bendable. 38/15/47 C-Clear (l. haze) Soit and rubbery. 38/15/47 ....do.. Soft and rubbery (not sticky). 40/0/60 Soit and rubbery. 40/0/60 Soit. 39/23/38 Soit and rubbery. 39/23/38 D0. 32/53/15 Hard. 50/40/10 D0. 55/25/20 5,5/25/20 Soit and rubber! (not sticky). 60/10/30 O-ODaque... Soit and rubbery 60/10/30 T-Turbid Soit and rub (not sticky) 16/70/15 0-0 ue.. White (greyish yellow).. Hard. 15/50/35 T-Turbid..... White 15/50/35 o1. .do., Soft and rubbery (sticky). 20/25/55 .-..do Grey 20/25/55 ...-do Light yellow Soit and rubbery.

c=snmp1e containing catalyst.

MN=Methacry1onltrile. VT=Vlnyltoluene. Ip=Is'oprene.

L.=Light.

Sl.=Slightly.

The compositions of samples 7 and 8 were selected to give monomeric mixtures lying fairly close to the line joining the two binary polymerization azeotropes, and on opposite sides of that line. Samples 9 to 14, inclusive, were prepared to cover a wide variety of compositions on either side of the line.

At the end of the polymerization cycle described above, all the polymers formed in the sealed tubes were carefully examined visually by the same observer, looking through the diameter of the cylindrical body of polymer obtained by breaking and removing the glass tube; this cylinder of polymer conformed to the internal shape and size of the glass tube. These visual observations were checked by other observers. It was determined that the clarity noted for polymer samples is not signitcantly affected by variation in polymer cylinder diameter within the range of about 14 to 18 millimeters. It is to be understood that where clarity of polymers is discussed herein, reference is made to the appearance on looking through a cylindrical body of the polymer having a diameter within the approximate range of 14 to 18 milli-` meters. The following words were adopted for describing the clarity of polymers.

C-Clear-essentially crystal clear H-Hazy-some cloudiness but slight T-Turbid-moderately cloudy O-Opaque-dense cloudinesssimilar to milk glass in appearance Referring now to Figure I of the drawings, the clarity data given for the catalyzed sample in Table I has been designated alongside each of the corresponding ternary monomeric mixture compositions indicated by a point on a triangular coordinate plot. The various numerals on Figure vI located adjacent to respective points refer to the sample numbers of Table I, the c however not being includedalongside the sample number in Figure I. All

`of the points marked C wererated as clear. A few of these points contained a slight haziness but not sucient to consider them other than essentially clear or to bring them from. the clear rating into the hazy rating.

.Examination of Figure I immediately shows that terpolymers preparedfrom. monomeric mixtures having compositions lying on the line joining the two binary azeotrope compositions were clear, as were terpolymers within the area lying along said line. However, the area of clarity is limited, as shown by turbid points 10 and 11 on one lside of the line and by opaque and turbid points 12, 13 and 14 on the other side of the line. It is interesting to note that the area of clear terpolymers extends a considerable distance from the line as indicated at clear point 9 which is about 16 percentage points away from the line in the direction of increasing methacrylonitrile content.

The data in the present example demonstrates that terpolymers made from ternary monomeric mixture whose com position is taken from along the line and from a significant area lying on leachy side of the line are clear.

A general statement can also be made about color in this terpolymer system (where the samples prepared from monomeric mixtures having compositions a considerable distance from the line in general are of more intense color than those samples prepared from mixtures .having compositions on or near the line. Thus, points 9,10, and 11'are orange or red, and points 12, 13, and 14 are largely white, as compared with the generally less intense yellows of the samples on or near the line.

In Figure I the dashed lines .drawn parallel to the line joining the two binary azeotrope compositions are percent on each side of the line, i. e., each is a distance from the line equal to 5 percentage points of composition as determined by dividing the distance between an apex and the center of the opposite side of the triangle into 100 equal equidistant parts; in other words, the two dashed lines are on opposite sides of and 5 graphical units distant from said line. Polymers made from ternary mixtures having compositions lying between these two 5 percent lines are preferred products of the invention. C

Example 2.-This example presents data on the ternary system methacrylonitrile/ styrene/ a-methylstyrene.

By the procedures used in Example 1, the composition of the binary polymerization azeotrope methacrylonitrile/ styrene was calculated, taking methacrylonitrile as M2 andstyrene as M1. The reactivity ratios used were r1=0.30 and r2=0.16. On this basis the binary polymerization azeotrope composition was 35 weight percent methacrylonitrile, 65 weight percent styrene.

By the same procedure, the binary polymerization azeotrope composition for methacrylonitrile/a-methylstyrene was calculated to be 43.4 weight percent methacrylonitrile, 56.6 weight percent a-methylstyrene.

Samples containing varyingproportions of the monomers were prepared and polymerized and observations made o n the polymers in the manner described in Example 1. The polymerization cycle was 24 hours at 90 C., 24 hours. at 120 C., 8 hours at 180 cycle for point 5 was 24 hours at 90 C., 41 hours at 120 C., 221/2 hours at 180 C. The data on compositions and polymer products are set forth in Table II, and shown graphically in Figure II of the drawings. No catalyst was kused in these tests.

TABLE II Methacrylonitrile/styrene/-methyIstyrene terpolymers MN=Methacrylonltrila -MS= -Methylstyrene. S styrene As in the other examples, the terpolymers prepared from monomeric mixtures whose compositions are on the line joining the two binary azeotrope compositions are clear. Furthermore, the area of clarity lying along the line is extensive. This clear area comes close to the line at point 11 which was turbid and which is only about 3 percent away from the line; point 11 is a binary methacrylonitrile/a-methylstyrene mixture. On the same side of the line but farther away, points and 21 are C. The

14 opaque. On the opposite side of the line, in the direction of decreasing methacrylonitrile content, point 22 was turbid and point 23 opaque. It is interesting to note also that these points at the greatest distance from the line, viz., points 21, 22, and 23, which points were not clear, also deviated from the yellow colorcharacterizing theother samples. Thus, point 21 was red and points 22 and 23 were white.

-As in Figure I, dashed lines have been drawn in Figure 1I which are 5 percent away from the line on each side of the line, and terpolymers prepared from monomeric mixtures whose compositions lie within these 5 percent lines are preferred products of the invention;4 Although polymers made from compositions lying close to point 11 yet within the 5 percentline are hazy, they are clearer and less opaquethan adjacent polymers beyond the 5 percent line. It will be apparent also that the area of clear terpolymers in general extends well` beyond the 5 percent lines.

While the invention has been described herein with particular reference to various preferred embodiments thereof, and examples have been given of suitable proportions and conditions, it will be appreciated that variations from the details given herein can be eiected with' of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene, a-methylstyrene, isoprene, butadiene, and (c) a different monomer rselected from said group, the proportions of ther three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of methacrylonitrile and the particular (b) on the one hand and methacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph. v f

2. A terpolymer according to claim 1 wherein one of said monomers is styrene.

3. A terpolymer according to claim l wherein one of` said monomers is vinyltoluene.

4. A terpolymer according to claim 1 wherein one of said monomers is a-methylstyrene.

5. A terpolymer according to claim 1 wherein one of said monomers is isoprene.

6. A terpolymer according to claim 1 wherein one of said monomers is butadiene.

7. A terpolymer according to claim 1 wherein said three monomers are methacrylonitrile, styrene, and amethylstyrene.

8. A terpolymer according to claim 1 wherein said three monomers are methacrylonitrile, vinyltoluene, and isoprene.

9. A clear terpolymer prepared by -free-radical-initiated batch mass polymerization of a monomeric mixture consisting of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene, a-methylstyrene, isoprene, butadiene, and (c) a different monomer selected from said group, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of methacrylonitrile and the particular (b) on the one hand and methacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

10. A terpolymer according to claim 9 wherein one of said monomers is styrene.

V14. A clear terpolymer prepared by, free-radical-in-` itiated batch polymerization to a conversion of at least 20 weight percent of a monomeric mixture yconsisting of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene, a-methylstyrene, isoprene, butadiene, and (c) a diierent monomer selected from said group, the proportions of the three monomers in said monomeric mixture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of methacrylonitrile and the particular (b) on the onehand and methacrylonitrile and the particularAv (c) ,on the other hand as plotted on an equilateral triangular coordinate graph.

15. A polymerization process which comprisesvforming a three-component monomeric mixture consisting of (a) methacrylonitrile, (b) a monomer selected from the group consisting of styrene, vinyltoluene, vinylxylene,

a-methylstyrene, isoprene, butadiene, and (c)` av diierent monomer selected from said group, the proportions of the three monomers in said monomeric mixtureV being limited to those in the area of mixtures thatproduce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of methacrylonitrile and the particular (b) on the one hand and methacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, and subjecting a batch of said monomeric mixture tofreeradical-initiated batch polymerization forming an essentially clear homogeneous high molecular weight terpolymer. r v

16. A polymerization processv according to' claim- 15 wherein said polymerization is effected in mass.4 t

17. A polymerization process according to claim, 1-5 wherein one of said monomers is styrene,

18. A polymerization process according to claim: 15 wherein said three monomers are methacrylonitrile, styrene, and a substituted styrene of said group.

19. A polymerization process according to claim 15 wherein said three monomers are methacrylonitrile, styrene, and a dioletn of said group.

20. A clear terpolymer prepared by free-radical-initiated batch polymerization of a monomeric mixturecon,

sisting of (a) methacrylonitrile (b) a monomer selected from the group consisting of styrene, vinyltoluene, vi`nyl.V xylene, a-methylstyrene, isoprene, butadiene, and (c)a different monomer selected from said group, the prt),-` portions of the three monomers in said monomeric vmilfv ture being limited to those in the area of mixtures that produce clear terpolymers, said area encompassing the line joining the polymerization azeotrope composition of methacrylonitrile andthe particular (b) on the one hand and methacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph, with the further. limitation that said proportions of the threev monomers are restricted to the area of said graph bounded by two lines on opposite sides of and parallel to and 5 graphical units distant from said line.

21. A clear terpolymer prepared by free-radicalin itiated batch polymerization of a monomeric mixture consisting of (a)` methacrylonitrile, (b) a monomer selected from the groupfconsisting of styrene, vinyltoluene, vinylxylene, a-methylstyrene, isoprene, butadiene, and (c) a dilerent monomerfselected from said-,grouplr the proportions of the three monomers in said` monomeric mixture being designated by the line joining thepolymerization azeotrope composition of methacrylonitrile and the particular (b) on the one hand and methacrylonitrile and the particular (c) on the other hand as plotted on an equilateral triangular coordinate graph.

22. A terpolymer according, to-claim 20 wherein` said three monomers are methacrylonitrile, styrene, anda:-v

methylstyrene.

23. A terpolymer according to claim 20 Ywherein said three monomers are methacrylonitrile, vinyltoluene, and isoprene. l

References Cited in the tile of this patent UNITED STATES PATENTS 2,384,543 Fryling Sept. 11, 1945 2,384,544 Fryling Sept. 11, 1945 2,527,162 Vanderbilt et al. Oct. 24, 1950 OTHER REFERENCES Alfrey et al.: Copolymen'zation, Interscience, 1952, pages 124-130. 

1. A CLEAR TERPOLYMER PREPARED BY FREE-RADICAL-INITIATED BATCH POLYMERIZATION OF A MONOMERIC MIXTURE CONSISTING OF (A) METHACRYLONITRILE, (B) A MONOMER SELECTED FROM THE GROUP CONSISTING OF STYRENE, VINYLTOLUENE, VINYLXYLENE, A-METHYLSTYRENE, ISOPRENE, BUTADIENE, AND (C) A DIFFERENT MONOMER SELECTED FROM GROUP, THE PROPORTIONS OF THE THREE MONOMERS IN SAID MONOMERIC MIXTURE BEING LIMITED TO THOSE IN THE AREA OF MIXTURES THAT PRODUCE CLEAR TERPOLYMERS, SAID AREA ENCOMPASSING THE LINE JOINING THE POLYMERIZATION AZEOTROPE COMPOSITION OF METHACRYLONITRILE AND THE PARTICULAR (B) ON THE ONE HAND AND METHACRYLONITRILE AND THE PARTICULAR (C) ON THE OTHER HAND AS PLOTTED ON AN EQUILATERAL TRIANGULAR COORDINATE GRAPH. 